The invention relates to a network system which mutually connects a plurality of LAN (Local Area Network) systems and relates to a connecting method among the LAN systems for such a purpose. More particularly, the invention relates to a network system which mutually connects a plurality of LAN systems having independent address schemas and relates to a connecting method among the LAN systems for such a purpose.
In a network system such as Internet, Intranet, or the like, a network protocol called TCP/IP is generally used. In the TCP/IP, by using IP addresses (Internet Protocol Addresses) in order to identify individual terminals which are connected onto the network, the mutual connection is realized. In the Internet, the addresses called global addresses which are allocated from JPNIC (Japan Network Information Center) and have uniquely set in the whole world are used as such IP addresses. In the LAN system closed in a certain organization such as a company or the like, the use of the global addresses which are allocated from the JPNIC is difficult because the problem of limitation of the number of addresses. In such an LAN system, therefore, addresses of terminals which are connected to the LAN system are set so as to be unique in the system in accordance with an address schema which was uniquely decided, a system of private addresses determined by the RFC (Request For Comment) standardized by the IETF (Internet Engineering Task Force), or the like.
Hitherto, generally, the LAN system in an organization constructed by using a network protocol such as TCP/IP or the like has been used only for the purpose of connection among the terminals in the organization. However, the access to the WWW server in association with the internet or the LAN connection through the internet or a dedicated line has spread and not only the connection among the terminals in the LAN system but also the mutual connection from a terminal of a self-sustaining LAN system to a terminal of another LAN system is increasing. As mentioned above, in the case where a terminal in a LAN system using a self address schema or a private address schema according to the RFC for the LAN system is connected to a terminal of another LAN system, usually, data on the LAN is capsulated by a global address of the internet and is transferred to the LAN system on the partner side, thereby realizing a mutual connection. Such a mutual connecting system of the LAN systems is generally called VPN (Virtual Private Network). Although the connection over the Internet is performed by the global addresses, addresses of terminals which are connected to each of the LAN systems which are mutually connected need to be uniquely determined in accordance with the same address schema. In many case, therefore, the connection among the LAN systems as mentioned above is limited to a connection among the LAN systems which are managed by the same organization.
In the case where the LAN systems which have already been used by different organizations, for instance, by enterprises A and B are mutually connected by the dedicated line or Internet, the address schemas are revised so that the addresses which are allocated to terminals which are connected to both of the LAN systems do not overlap in consideration of the address schemas which are used in the LAN systems, and if the uniqueness of the addresses is assured, the mutual connection of those LAN systems can be realized.
For example, in JP-A-6-209323, there has been disclosed a communication system such that in the case where the LAN systems constructed by different address schemas are connected by an intermediate apparatus, all of the LANs which are connected to the intermediate apparatus are regarded as one network without changing the address schemas of the LAN systems, an address schema of the whole network in which the addresses become unique is set, a mapping among the address schemas of the individual LAN systems and the address schema of the whole network is performed, and they are mutually connected.